Long term growth in grass yields utilisation will be difficult, say scientists

Scientific predictions indicate a good increase in the total annual gras yield on Northern Ireland farms over the coming decades but with the risk of possibly more difficult utilisation due to higher rainfall.

The latest data was unveiled at the AFBI open days for farmers at Hillsborough last week with Tuesday organised for dairy farmers and Wednesday for beef and sheep farmers.

The data says that for every one-degree celsius rise, rainfall will increase by seven per cent.

AFBI used the AFBI GrazeGro model over a 200-year period from 1900 to 2100 to evaluate both past and future patterns of grass growth under the UK Met Office UKCP18 climate change projections. The trend will be for an extended growing season but more difficult utilisation.

The increase could be by almost two tonnes of DM per ha by 2050 due to rising temperatures but with a similar level of volatility expected.

One measure to help farmers cut costs will be the increased use of red and white clovers which use nitrogen from the air. Some AFBI plot trials have found that red clover monocultures could produce yields of 18t DM/ha without nitrogen fertiliser in their first year.

For a typical 100-cow dairy farm, with a 25 per cent conversion of silage area to red clover, this would equate to a saving of seven tonnes of 27 per cent N fertiliser saving £2,300 and reducing N2O emissions by 40 tCO2e.

Other AFBI research using white clover has found that grazed swards with 30 per cent white clover content can fix 150kgN/ha/year from the air.

Although the growth of white clover can be slower in spring compared to grass (since it requires a soil temperature of 8°C compared with the 5°C requirement of grass), during the mid to late season white clover peaks as grass growth declines.

This complementary growth pattern delivers enhanced sward resilience and can reduce fertiliser N input by 65 per cent, thus curbing N2O emissions by 39 tCO2e and saving £2,200 in fertiliser with 25 per cent conversion of grazing.

Other messages from AFBI Hillsborough were the importance of soil health to maximise nutrient use efficiency.

Suzanne Higgins and Lisa Black from AFBI said soil health was determined by its chemical, physical and biological status.

They say that soil is healthy when it is in good chemical, biological and physical condition and able to sustain plants, animals and humans as part of a thriving ecosystem.

Across Northern Ireland (NI), soil health is directly impacted by how it is managed on farms in terms of nutrient inputs, ploughing and reseeding and by environmental factors such as climate, topography and geology.

In managed systems, soil health can be maintained, promoted or recovered through the implementation of sustainable soil management practices and by avoiding soil degradation.

When a soil is healthy and in good condition, nutrient use efficiency by crops will improve, with a greater economic return on slurry and purchased inorganic fertiliser applications.

Healthy soil will have a greater ability to adapt to existing conditions as well as to a changing environment.

This is particularly important considering the recent trend towards wetter, milder winters, periods of drought during summer and increased frequency and intensity of storm events.